1. Field of the Invention
The present invention relates to a semiconductor laser module and an optical amplifier installing the same. More particularly, the present invention relates to a semiconductor laser module adequate for a pumping light source in an optical amplifier and the optical amplifier installing the same.
2. Description of the Related Art
A high output greater than hundreds of mW is required for laser modules as a pumping light sources in optical amplifiers. Therefore, it has been an extremely important problem to dissipate the heat generated in a semiconductor laser chip because a large drive current is injected to the chip.
Such semiconductor laser modules as pumping light sources generally employ a so-called butterfly type package. FIG. 4 is a sectional view of a typical semiconductor laser module using the butterfly type package mentioned above.
As shown in FIG. 4, a semiconductor laser chip 35 is mounted on a submount 31, the submount 31 is mound on a base 30, and the base 30 is mounted on a cooling means 34. These members including the base 30, the submount 31, the cooling means 34 and the semiconductor laser chip 35 are integrally contained in a package 10. In this case, the package 10 is made of metal material such as nickel-Kovar.
The package 10 is substantially cubic and has a window on one side wall. An optical fiber 20 is projected from the window into the package 10 via a sleeve 22. The sleeve 22 contains a ferrule 21 fitted to the front end of the package 10. The center axis of the sleeve 22 and the center axis of the ferrule 21 are arranged in such a manner that their relative positions are regulated, so that the optical axis of the optical fiber 20, which substantially conforms to the center of the ferrule, is efficiently coupled to the semiconductor laser chip 35.
A condenser lens 32 is disposed on the light axis. Moreover, a light-receiving element 33 is disposed in the rear of the semiconductor laser chip 35 so as to control the drive current to the semiconductor laser chip under so-called APC (Auto Power Control).
As the cooling means, a Peltier element is often employed. By the current passing therethrough, a one-side electrode thereof (simultaneously used as the base 30) is cooled and the other electrode side in contact with the package is heated.
FIG. 5 is a plan view of the package used in the semiconductor laser module shown in FIG. 4.
As shown in FIG. 5, the package 10 is rectangular as viewed from above and the optical fiber 20 fixed via the sleeve is projected from one edge face thereof. A plurality of lead pins 11 are led out from a pair of opposed sides of the package 10. These lead pins 11 include a power supply line toward the semiconductor laser, a drive signal line, a light-receiving signal line from a monitor PD, a power supply line toward the Peltier element, a detection signal line for detecting the temperature of the upper electrode of the Peltier element and so forth.
Although the butterfly package has a large internal space for containing the Peltier element therein, it has problems that the package itself is large in size and has to be made of expensive metal material. Further, although the package made of metal satisfies requirements of high-performance for semiconductor laser modules, it has a problem that an insulating process is needed for the lead pins. Nevertheless, this type of semiconductor laser modules are very expensive and not necessarily high in productivity, that is, not fit for mass production.
However, optical amplifiers using erbium doped fibers (hereinafter called xe2x80x98EDfxe2x80x99) have used in not only trunk lines but also subscriber lines in recent optical communication systems. Therefore, the mass production for semiconductor laser modules as pumping light sources is required. Moreover, the size-reduction is required rather than the mass production in the subscriber line system. Accordingly, the conventional semiconductor laser modules do not meet the requirement for size-reduction.
An object of the present invention to provide a semiconductor laser module that can be mass-produced less costly and reduced in size and an optical amplifier installing the same that can be mass-produced less costly.
A semiconductor laser module according to the invention comprises a light-emitting element, a package, an optical fiber and a ferrule. The light-emitting element has a reflective surface and an antireflective surface at opposed edge faces. The package houses the light-emitting element therein. The optical fiber has a diffraction grating optically coupled to the antireflective surface of the light-emitting element. The reflective surface of the light-emitting element and the diffraction grating formed in the optical fiber form an optical resonator. The ferrule is secured relative to the package and holding an end portion of the optical fiber therein. The light-emitting element is mounted on the package without providing a temperature control member therebetween, and the diffraction grating is formed close to the end portion of the optical fiber so as to be positioned within the ferrule.
The semiconductor laser module according to the invention preferably includes light concentrating member provided between the light-emitting element and the optical fiber.
In the semiconductor laser module according to the invention, the reflective bandwidth of the diffraction grating may be selected to include a plurality of longitudinal modes of the light-emitting element. The longitudinal modes thereof are determined by the distance between the reflective surface and the antireflective surface of the light-emitting element. The central wavelength of the bandwidth may exist substantially in a 1.48 xcexcm band.
The semiconductor laser module according to the invention may further include an amplifying optical fiber with erbium doped in a predetermined portion of a core thereof, and a light-introducing member introducing the light emitted from the optical fiber into the amplifying optical fiber. This semiconductor laser module may also functions as an optical amplifier for amplifying signal light having a wavelength in a 1.55 xcexcm band.